My brownie recipe is from a cookbook and I tried a lot of variations on it and then had to concede that the person who wrote the recipe got it just right. I make it with high quality chocolate and butter and then am very careful not to over bake it and they turn out deliciously decadent every time!
For those moments you just can't wait for them to cool, although, even cooled a good moist brownie tends to stick to the knife.
Part of this phenomena comes from 20th century cooking (especially for sweets): the ingredients are mass produced to high standards of consistency, and hence there may be one just right recipe (especially if you're backing in a climate controlled kitchen at sea level). Consider, instead, artisanal bread baking in 2018. Your flour comes from a food coop which used to get it stone ground by an Amish cooperative, but now switched suppliers to a local farmer -- and the recipe needs to change. Your sourdough starter turned acidic because you went away on vacation and it sat in the fridge -- change the recipe again! It's an unusually damp and chilly day, and the loaf is sitting out during its second rise -- you'll need to change the recipe!
Of course this is part of the thrill of this sort of baking -- that you have to understand the underlying processes, not just the well-made building blocks, to end up with good results. Sort of like switching from running OS X or Windows to, say, Linux from Scratch...
First, there was a money-saving switch from lard to commercial shortening or margarine. Either one was made of partially hydrogenated vegetable oil.
Second, due to trans fats or a desire to be less fake, that got switched to butter.
Lard makes wonderful brownies. Compared to butter, the taste comes out far cleaner. The purity of the chocolate really comes through.
Another fine option is coconut oil.